The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Photographic stereoscopy is a well known technique used by military and civilian air photo analysts while studying ground scenes to obtain intelligence information. The photos are ordinarily taken by a reconnaissance camera carried on an aircraft and aimed at or near perpendicular to the flight path of the aircraft. Only one camera is needed, and it is aimed vertically downward in mapping applications or obliquely (i.e., 90 degrees relative to the direction of travel of the aircraft) toward the horizon for standoff. The camera takes pictures at time intervals, producing a series of images. View fields of adjacent images overlap to produce the stereo effect. During photo interpretation, two different images showing the same scene are arranged side-by-side for stereoscopic viewing. They can also be specially processed to form an anaglyph.
Laser Detection and Ranging (LADAR) and Light Detection and Ranging (LIDAR) are methods of obtaining an image in which each pixel is accompanied by a range measurement. With LADAR, an active light source is required, and range information is obtained for each pixel by measuring the transit time of the illumination pulse. Each image pixel has measurements that locate it in three dimensional space. A LADAR image can be viewed as a normal photograph such that points in the scene are color-coded based on distance from the camera. The LADAR image can also be rotated by computer graphics functions for viewing from different angles. Rotation results in gaps in the image. The gaps represent scene volumes obscured by foreground surfaces as viewed by the sensor at the acquisition location.
Imaging LADAR has three variants. The first, “Scanning LADAR,” may use a laser to paint the scene like the electron gun in a vacuum tube television. The second, “Flash LADAR,” makes use of a wide beam laser that illuminates the entire scene at once, and each pixel calculates its own light transmission time. The third, “Streak-tube LADAR,” uses a fan shaped laser beam to illuminate either a row or a column of scene pixels at one time, and scans across the scene using sequential bursts of illumination. Imaging Synthetic Aperture Radar (SAR) and imaging SONAR are also similar to LADAR in their methods and products.
One limitation of the existing photographic stereoscopy process is that the views are limited to being oriented at angles near perpendicular to the flight path of the airborne mobile platform (e.g., aircraft) from which the images are being taken. A second limitation is that the existing stereoscopic solution requires the scenes in the two photos to be at or near the same size.
Another limitation of the existing LADAR solution is its current state of development, which complicates evaluation of its effectiveness. Still another limitation is the absence of non-topographic surface texture in the target's image. Yet another limitation is that LADAR is not presently in common use.